1. Field of the Invention
This invention relates to a disc cartridge having a disc-shaped recording medium accommodated therein. More particularly, it relates to a disc cartridge having a shutter mounted thereon for opening or closing a signal recording/reproducing aperture(s) formed in a cartridge main body.
2. Description of the Related Art
As an optical recording medium for musical sound, picture or other information signals, there has hitherto been employed a read-only optical disc on which desired information signals, such as musical sound information signals, are recorded previously for reproduction after loading the disc on a reproducing apparatus by the user.
As an optical recording medium in which prerecorded signals may be erased and re-recorded, there has also been proposed a magneto-optical disc in which a magnetic thin film is used as a recording layer.
With the optical recording media, such as the optical or magneto-optical discs, recording and/or reproduction of information signals of an extremely high density is possible because a laser beam is employed for recording and/or reproduction of information signals. For example, with an optical disc devoted to reading of prerecorded information signals, reproduction of musical sound signals continuing for about 74 minutes is possible with a disc which is 12 cm in diameter. Recording of information signals of substantially the same volume as that of the optical disc is possible with the optical disc.
Meanwhile, there is also proposed an optical disc or a magneto-optical disc with which a higher recording density may be achieved. For example, there is proposed a method of recording information signals after signal compression for improving the recording density.
With a higher recording density, it becomes possible to record the same volume of information signals as that recorded on a conventional optical recording medium on an optical recording medium of a smaller diameter.
On the other hand, with the optical or magneto-optical disc, with which a higher recording density may be realized, the slightest scores or deposition of the smallest amount of foreign matter on the signal recording surface results in marked deterioration in recording and/or reproducing characteristics.
For this reason, this type of the optical recording medium needs to be accommodated in a sealable cartridge to prevent scoring or deposition of foreign matter during recording, handling or during storage when the recording medium is not loaded on the recording and/or reproducing apparatus. The optical recording medium needs to be accommodated reliably in and protected by the cartridge during storage.
On the other hand, it is required of the recording/reproducing apparatus, having the optical recording medium, thus reduced in size on account of the improved recording density, as a recording medium, to be similarly reduced in size in order to keep up with the reduction in size of the optical recording medium.